A heat recovery ventilator (HRV) is a mechanical device that incorporates a heat exchanger with a ventilation system for providing controlled ventilation into a building. The heat exchanger heats or cools incoming fresh air using exhaust air. Energy/Enthalpy Recovery Ventilators (ERV) can exchange moisture in addition to heat between two air streams. ERV systems typically include a sheet metal enclosure, fans to move the air streams, ducting, filters and control components. A key component in an HRV/ERV that transfers the heat and water vapour between the air streams is called the core. A core is typically constructed using a plurality of plates that are stacked, sealed and configured to accommodate fluid streams flowing in either cross-flow or counter-flow configuration between alternate plate pairs, so that heat and water vapour are transferred via the plates. Planar plate-type cores for HRV/ERV implementations and other applications are readily scalable. However, meeting high efficiencies targets is a challenge using conventional designs.